Hollow golf club head

ABSTRACT

A hollow golf club head includes: a metal head main body including a hollow section; and a weight formed from magnesium or a magnesium alloy in at least one of a toe side, a heel side, a back side and a sole of the metal head main body.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a hollow golf club head which generates superior feeling of hitting and a superior hitting sound.

2. Description of the Related Art

A metal golf club head having a hollow section has become larger in size. Of so-called drivers head having a loft angle of 13° or less, a driver head having a head volume of 300 cc or more, particularly 350 cc to 500 cc, has come predominant. In the case of the driver head, a head weight is 200 g or less and preferably ranges from 180 g to 195 g or thereabouts; and the specific gravity of a titanium alloy ranges from 4.2 to 5.0. Hence, a crown, sides, and a sole are made smaller in thickness. In some cases, partially reducing the thickness of a face has hitherto been performed.

In a heretofore driver head which is formed from a titanium alloy (e.g., Ti-6Al-4V) through casting and has a hollow section, each of a crown, a sole, and sides has a thickness of about 1.2 mm, and a face has a thickness of about 3 mm. Recently, portions (a sole, sides, a crown, a face, or a part formed integrally from two or more of these portions) of a golf club head are formed by means of pressing a plate material, such as a β-type titanium alloy, and the like; and these portions are welded together, to thus manufacture a golf club head having a hollow section, as disclosed in JP-A-2003-52866. In relation to casting, there has been adopted a method for melting metal by means of a lost wax method (an investment casting method) and pouring the melt metal into a ceramic mold. Difficulty is encountered in reducing the thicknesses of respective portions. However, a method for forming respective portions of a golf club head by means of pressing enables a reduction in the thicknesses of the respective portions. Hence, a thickness of 1 mm or less becomes feasible, which has enabled manufacture of a larger golf club head.

SUMMARY OF THE INVENTION

However, as a result of a reduction in the thickness and an increase in the size of the golf club head, vibrations developing in the golf club head when the club head hits a golf ball become greater, which unpreferably affects the feeling of hitting and hitting sound.

The present invention is conceived in view of the circumstances and aims at providing a hollow golf club head which generates enhanced feeling of hitting and hitting sound.

In order to achieve the object, the present invention provides a hollow golf club head including: a metal head main body including a hollow section; and a weight formed from magnesium or a magnesium alloy in at least one of a toe side, a heel side, a back side and a sole of the metal head main body.

The hollow golf club head of the present invention effectively dampens vibrations of the golf club head resulting from hitting of a golf ball by means of the weight formed from magnesium or a magnesium alloy, and enhanced feeling of hitting and enhanced hitting sound are achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view showing a head main body of a hollow golf club head of an embodiment of the present invention, and FIG. 1B is a cross-sectional view of the head main body taken along T1-T1 shown in FIG. 1A;

FIG. 2A is a perspective view of the head main body when viewed from a direction differing from that where FIG. 1A is acquired, and FIG. 2B is a cross-sectional view of the head main body taken along T2-T2 shown in FIG. 2A; and

FIG. 3 is a graph showing a relationship between vibration frequencies and damping ratios of golf club heads of an embodiment and comparative examples.

DETAILED DESCRIPTION OF THE EMBODIMENTS

An exemplary embodiment of the present invention will be described in detail below. In the exemplary embodiment, no limitations are imposed on the material of a metal head main body having a hollow section. However, for example, a titanium alloy, stainless steel, an aluminum alloy, and the like, are mentioned. The metal head main body may also be formed integrally by means of casting or connecting a plurality of parts through welding or the like.

No limitations are imposed on the type of a metal head main body employed in the exemplary embodiment. A light-weight driver head having a small thickness is particularly preferable. For instance, a driver head, which is formed from, e.g., a titanium alloy (of, e.g., a specific gravity of about 4.5) or an aluminum alloy (of, e.g., a specific gravity of about 2.7) and has a head volume of 300 to 500 cc, can be preferably used. In the case of a head formed from stainless steel having large specific gravity (for example, a specific gravity of 7.8), a driver head having a head volume of 200 to 300 cc can be used preferably. In relation to the thickness of the head, the least thickness of the crown, the sole, and the sides is appropriately set to 0.5 mm to 1.0 mm, particularly 0.6 mm to 0.9 mm.

In the exemplary embodiment, the type of the magnesium alloy is not limited. An alloy made by adding aluminum and zinc to magnesium can be preferably used. More specifically, an AZ31 alloy made by adding 3 percent by mass aluminum and 1 percent by mass zinc to magnesium, an AZ61 alloy made by adding 6 percent by mass aluminum and 1 percent by mass zinc to magnesium, an AZ91 alloy made by adding 9 percent by mass aluminum and 1 percent by mass zinc to magnesium, and the like, can be used preferably. However, the magnesium alloy is not limited to them.

The weight which is used in the present embodiment and formed from magnesium or a magnesium alloy preferably has a weight of 1 to 5 grams. When the weights are too light in weight, an effect of damping vibrations of the head is not achieved. In contrast, when the weights are too heavy in weight, the weight of a head is affected undesirably. The specific gravity of the magnesium alloy is of the order of 1.7 to 2.0 or thereabouts. The Young's modulus of the magnesium alloy is 44 to 45 Gpa which is one-half or less the Young's modulus of the titanium alloy or about 60 to 70 percents of the Young's modulus of the aluminum alloy.

Since magnesium or the magnesium alloy is susceptible to corrosion, the surface of the weight may also be subjected to corrosion treatment. Specifically, the surfaces of the weights can be subjected to corrosion treatment by means of chromate treatment, chemical conversion treatment such as selenite treatment, anodizing, and the like, or the surfaces of the weights can be subjected to corrosion treatment by means of coating the surfaces with insulating coating or an insulation resin.

In the exemplary embodiment, no limitations are imposed on the manner where the weight is placed in the metal head main body. For instance, a recess is formed in either sides and a sole of the metal head main body or both the sides and the sole of the same, and a weight is fixed to the recesses. An opening is formed in either the sides or the sole of the metal head main body or both the sides and the sole of the same, and the weight can be fixed to the openings. In this case, a thick portion is formed in either the sides or the sole of the metal head main body or both the sides and the sole of the same, and forming the recess or the opening in the thick portions is preferable. Moreover, the recess preferably protrudes from an exterior surface of the head main body to the hollow section of the head main body. In addition, it is better to form the weight into a screw having an external thread, form a female screw in the recess or opening formed in the thick portions, and screw-engage the weight with the recess and the opening.

According to the hollow golf club head of the exemplary embodiment, preferable feeling of hitting and preferable hitting sound can be acquired.

An embodiment of the present invention will be described by reference to the drawings. However, the present invention is not limited to the embodiment provided below. FIG. 1A is a perspective view showing a head main body of a hollow golf club head of an embodiment of the present invention; FIG. 1B is a cross-sectional view of the head main body taken along T1-T1 shown in FIG. 1A; FIG. 2A is a perspective view of the head main body when viewed from a direction differing from that where FIG. 1A is acquired; and FIG. 2B is a cross-sectional view of the head main body taken along T2-T2 shown in FIG. 2A.

A head main body 10 of the present embodiment has a sole 12, a crown 14, a toe side 16, a heel side 18, and a back side 20. A hollow section 22 is formed in the head main body 10, and an opening section 23 closed by a face member is formed in a face side of the head main body 10. In the head main body 10 of the present embodiment, the toe side 16 has a recess 24, and the heel side section 18 is provided with a recess 26. The recesses 24 and 26 protrude from an exterior surface of the head main body 10 into the hollow section 22 of the head main body 10, and tip ends of the recesses are opened. Each of the recesses 24 and 26 has a large-diameter portion 28 on the exterior surface side of the head main body 10, and a small-diameter portion 30 is provided at an end of the large-diameter portion 28. A female thread is formed along a circumferential surface of the small-diameter portion 30. A weight 32 formed from magnesium or a magnesium alloy is fitted to each of the recesses 24 and 26. The weight 32 is a screw which has a large-diameter section 34 corresponding to the large-diameter sections 28 of the recesses 24 and 26 and a small-diameter section 36 corresponding to the small-diameter sections 30 of the recesses 24 and 26 and which has an external thread formed in the circumferential surface of the small-diameter section 36. The screw 32 is fixed to the head main body 10 by means of screw-engaging the small-diameter section 36 with the small-diameter sections 30 of the recesses 24 and 26. In the drawing, reference numeral 38 designates a shaft insertion section.

In this embodiment, a weight is provided in the toe side section and the heel side section, respectively. However, the location where the weight is to be provided in the present invention are not limited to these locations. A weight can be disposed, as appropriate, at one or two or more locations selected from the sole 12, the toe side section 16, the heel side section 18, and the back side section 20.

A head main body of a hollow golf club head of the embodiment shown in FIGS. 1A to 2B is manufactured. In this case, the head main body is formed from a Ti-6Al-4V titanium alloy by means of investment casting. A face member is formed from a β-type titanium alloy by means of pressing. A weight is formed from a magnesium alloy (an AZ61 alloy). A face member is fixed to the head main body by means of welding, and the weight is fixed into each of two recesses of the head main body, thereby completing a golf club head. In the hollow golf club head of the present embodiment, a head volume is 460 cc; the least thickness of the crown is 0.6 mm; the least thickness of the sole is 0.9 mm; and the least thickness of the sides is 0.7 mm. The face member is a thick face member having a thickness of 2.6 mm to 3.6 mm. The side where the recess is formed is made thick.

A golf club is manufactured by use of the hollow golf club head. Feeling of hitting and hitting sound is evaluated by means of actual hitting of a golf ball by a golfer. Similar evaluation is also performed by use of a hollow iron golf club head (Comparative Example 1) where screws formed from nylon are fixed as a weight to the respective two recesses and a hollow iron golf club head (Comparative Example 2) where screws formed from stainless steel are fixed as a weight to the respective two recesses. The weight of the screw formed from a magnesium alloy is 1.5 g/piece; the weight of the screw formed from nylon is 0.9 g/piece; and the weight of the screw formed from a stainless steel is 6.5 g/piece. Consequently, evaluation by the golfer is as follows.

Hollow Golf Club Head of the Embodiment

Hitting sound between hitting sound generated by the club head using the screws formed from stainless steel and hitting sound generated by the club head using screws formed from nylon

Sound is not muffled, and a high-pitched sound is generated.

Only sound echoed.

Optimum feeling of a ball being repelled by a face

Hollow Golf Club Head of Comparative Example 1

Sound is muffled.

Mild but insufficient feeling of hitting

Feeling of hitting is not transmitted well

Sound did not echo, and less feeling of hitting is transmitted. No feeling of far flying of a ball is acquired

Hollow Golf Club Head of Comparative Example 2

Sound echoed, but the head felt hard.

High-pitched sound

Feeling of a ball being repelled by a face and departing quickly

Difficulty seemed to be encountered in controllably hitting a ball

A relationship between the oscillation frequency of the head and an attenuation ratio is examined through modal analysis by use of the golf club head of the embodiment, the golf club head of Comparative Example 1, and the golf club head of Comparative Example 2. Modal analysis is an analytical technique which will be described below. Specifically, when force is exerted on a structure from the outside, the structure starts and keeps vibrating continually. The vibrations have a characteristic shape (a characteristic mode). Vibrations arise at a characteristic frequency (characteristic vibrations) and attenuate (a modal damping ratio). Modal analysis is an analytical technique for determining characteristic dynamic properties (modal parameters); namely, a characteristic mode, characteristic vibrations, and a mode damping ratio. In this test, vibration characteristics of the golf club heads are evaluated by means of modal analysis through use of an impact hammer. Results of the test are plotted in a graph of FIG. 3.

The golf club head of the embodiment using the screws formed from a magnesium alloy is understood to be higher, at low frequencies, in damping ratio than the golf club head of Comparative Example 2 using the screws formed from stainless steel. The golf club head of the embodiment is understood to be, at high frequencies of 5000 Hz or more, equal in damping ratio to the golf club head of Comparative Example 2 using the screws formed from stainless steel and to exhibit an appropriate vibration damping characteristic. In contrast, the golf club head of Comparative Example 1 using the screws formed from nylon is understood to be high in damping ratio at all frequencies and to exhibit an excessively-high vibration damping effect. The golf club head of Comparative Example 2 using the screws formed from stainless steel is understood to have a low damping ratio at all frequencies and to exhibit a low vibration damping effect. 

1. A hollow golf club head comprising: a metal head main body including a hollow section; and a weight formed from magnesium or a magnesium alloy in at least one of a toe side, a heel side, a back side and a sole of the metal head main body.
 2. The hollow golf club head according to claim 1, wherein: a recess is formed in at least one of the toe side, the heel side, the back side and the sole of the metal head main body, wherein the weight is fixed to the recess.
 3. The hollow golf club head according to claim 1, wherein: an opening is formed in at least one of the toe side, the heel side, the back side and the sole of the metal head main body, wherein the weight is fixed to the opening.
 4. The hollow golf club head according to claim 1, wherein the weight is a screw. 